There has been a shift in recent years in dentistry from a philosophy of drilling and filling to one of prevention and cosmetics. Due to concerns about the visual appearance of their teeth, many people undergo clinical procedures to enhance their smile or to correct certain dental defects. Clinical or cosmetic procedures of this type generally involve the modification of tooth shape, alignment and, more recently, color.
A necessary step in the modification of a patient's tooth color is to determine the "shade" of an existing tooth. Such a determination is useful, for example, to patients seeking a whiter, brighter smile, who frequently want a record of their existing tooth color so they can make a before and after comparison. Shade determination is even more important when reconstructive work is done, since one goal of the process is to achieve a natural appearance. To this end, it is necessary to know the existing tooth shade so that it can be accurately matched with the new restoration.
At present, with respect to tooth color modification, most dentists utilize standardized shade guides created by companies which manufacture reconstructive materials. One well-known shade guide is the VITA.TM. shade guide, which includes sixteen different shades. Other, shade guides used in practice include the guides provided by BIOFORM.TM. and SR-VIVADENT.TM..
For the most part, the existing shade guides are still utilized in a rudimentary fashion. The guide itself is a plastic plate with a plurality of removable color tabs that are shaped like a tooth, e.g., the front tooth. Typically, to assess a patient's tooth shade, a dentist removes one or more of the colored tabs and holds them up to the patient's tooth to "eyeball" the closest match. Understandably, this approach sometimes fails, in part because of the need for a subjective assessment by the dentist, who may not be sufficiently qualified for the task.
Another problem with the currently prevailing procedure is that once the tooth shade is determined, the information must be communicated correctly to the lab that makes the crown, bridge or denture. As known in the art, in bonding or filling a tooth, for example, the composite materials required for the restoration are specified within the range of the shade guide, e.g., one of sixteen shades for the VITA.TM. range. Errors in the determination of the tooth shade, or the communication of the determined shade to the lab will result in a poor shade match for the patient. For example, some dentists use uncommon shade guides, thereby leaving it to the lab technician to eyeball and convert the shade information to a VITAT.TM. standard shade (since porcelain is often made from the VITA.TM. shade guide). This too can result in improper shade matching.
The process for selecting the porcelain for a particular tooth shade illustrates the difficulty in assessing and manufacturing the correct color match. If, for example, a crown of VITA.TM. shade A3 is desired, porcelain is built by hand with a paint brush onto a model of the tooth to be restored. The porcelain is built in layers on the model to achieve translucency and natural appearance. Each layer has a particular color and intensity associated with it. To generate shade A3, the technician follows a "recipe" that is given by the manufacturer VIDENT.TM., requiring a different shade for each layer of porcelain applied. If a doctor asks for a shade that is not a VITA.TM. standard shade, the technician typically seeks to achieve that shade by combining different porcelain shade combinations together, to increase or decrease the chroma, hue and value of the shade.
To further complicate the color-matching process, some dentists are simply not skilled in taking and determining shade information. Therefore, these dentists sometimes send their patients directly to the lab where the technician can determine the shade information. Alternatively, these dentists sometimes have a technician come to their office. In either event, there is, at times, one more level of subjective uncertainty injected into the correct match and determination of a patient's tooth shade. It was apparent, therefore that there is a need for improvements in this area.
In the prior art, several attempts have been made to measure tooth shade. Such prior art includes, without limitation, the following patents and publications, each of which is incorporated by reference as providing useful background information: JP 4-338465 by Kazeo Eto; JP 4301530 by Kisaka; U.S. Pat. No. 3,986,777; U.S. Pat. No. 4,247,202; U.S. Pat. No. 4,414,635; U.S. Pat. No. 4,518,258; U.S. Pat. No. 4,547,074; U.S. Pat. No. 4,623,973; U.S. Pat. No. 4,654,794; U.S. Pat. No. 4,692,481; U.S. Pat. No. 4,836,674; U.S. Pat. No. 4,881,811; U.S. Pat. No. 5,012,431; U.S. Pat. No. 5,124,797; U.S. Pat. No. 5,231,472; U.S. Pat. No. 5,240,414; U.S. Pat. No. 5,313,267; U.S. Pat. No. 5,343,267; U.S. Pat. No. 5,373,364; U.S. Pat. No. 5,383,020; U.S. Pat. No. 5,690,486; U.S. Pat. No. 5,759,030; WO 86/03292; WO 91/02955.
Generally, the attempts to measure tooth shade, as disclosed in the illustrative prior listed above, fail for various reasons, including primarily color contamination due to reflection and/or tooth translucency. In addition to inconsistent and sometimes inadequate and unreliable tooth shade determination, methods and devices disclosed in the prior art also have other limitations. For example, prior art using colorimeters often samples a single tooth location in attempt to analyze its color. Such an approach, however, fails to adequately characterize the entire spatial extent of the tooth, much less address the issue of matching the shade of one tooth to the shades of adjacent teeth.
PCT Application W097/01308 and U.S. Pat. No. 5,766,006 ("the '006 patent") addresses many problems associated with the prior art. In particular, it discloses a camera that connects to an electronic shade analyzer system. The camera captures a digital color image of a tooth and compares that image to a stored plurality of tooth shades. Once a match is determined, the matching tooth shade is communicated to a user of the system, so that the desired tooth can be constructed. The methodology disclosed in the patent also includes the specification of fractional tooth shades. It will be appreciated that the approach discussed in the '006 patent is a substantial improvement over the prior art at least in terms of removing several levels of subjectivity.
Despite the significant advances achieved over the years, it is perceived that there is a need for improvements in several important areas. For example, these areas include the methods for digital signal processing which minimize the probability of matching errors due to various system imperfections. Another area where further improvements are desirable is the data capture process. By means of an example, it will be appreciated that it is very difficult to capture information about a tooth or groups of teeth that is independent of the lighting conditions, or the particular camera used. Accordingly, there is a need for improvements in several areas related to optimal analysis and processing of tooth shades.